Coordination of the cytoskeletons of neighboring cells is an important component of morphogenesis during development. As a model system to study this coordination, I am using the Drosophila epidermis, a tissue that elaborates large numbers of hairs and bristles. These are polarized structures formed from cytoskeletal-mediated projections of epidermal cells. Hairs and bristles are normally aligned in parallel giving the tissue a distinct polarity. Our observations indicate that cell geometry plays an important part in the development of tissue polarity. It is proposed to determine how this is altered in tissue polarity mutations. It is my long term goal to understand on a molecular level how tissue polarity is achieved, and what the roles of individual genes and gene products are in the process. I have been examining the function and structure of a particular genetic locus (frizzled (fz)) that is essential for the development of normal tissue polarity. Mutations in this gene result in an epidermis where hairs and bristles are no longer aligned in parallel, and where they no longer point in the normal direction. Mitotic clone experiments indicate that fz function is needed for both the transmission of polarity information, and for cells to respond to the information. In developing epidermis the fz gene appears to encode a single protein that contains 7 transmembrane domains. It is proposed to complete the structural characterization of the fz gene and it transcripts, and to complete the analysis of the tissue specific pattern of fz expression. Protein domain specific antibodies will be raised, and they will be used to determine the topology of the fz protein. The amino acid changes associated with fz mutations will be determined as a first step in defining a functional map of the protein. Experimental systems will be developed that can be used to test if any of the known transduction pathways or second messengers are involved in the development of tissue polarity, and for future studies to determine the function of particular amino acids and protein domains.